1. Field of the Invention
This invention relates to a film image reading apparatus for reproducing an image recorded on an original sheet film by reading the image of the original sheet film as projected on the main unit of the image reading apparatus by means of a projector, and more particularly to a density correcting system which is to be used for the film image reading apparatus and to perform the correction of density in the color decomposing signals of the film image as transmitted from the optical system.
2. Description of the Related Art
In order to reproduce the images recorded on various types of film, such as 35-mm film, in the form of prints having a desired size, it is in general practice to obtain prints of such images by printing the images on photosensitive paper. However, this process of printing such images on sensitive paper requires highly specialized techniques, as well as special equipment and facilities. Thus, it has hitherto been impossible for laymen to perform such printing work in any handy way. In addition, as the price for such prints is fairly expensive, it has not been economical to have film images reproduced on such prints having a specific desired size.
Recently, the progress attained in the color copying machines has made it possible to employ such a color copying process in making highly precise color reproductions of images recorded on paper. In addition to this, with an objective of providing a color copying machine capable of responding positively to the users' requirements, considerable progress has been made in the development of multiple functions in color copying machines such as improved color-reproducing capabilities, improved precision in the reproduction of details, and synthesis of images. This progress is also due to the development of various types of image processing techniques, such as enlarging and reducing functions, which have been accomplished by the processing of digital signals used to represent the images.
In view of these developments, it has been proposed to perform the color copying process with a digital copying machine using image signals obtained by projecting with a film projector the images recorded on various types of film and by obtaining electrical image signals by reading the projected images with an image reading system equipped with a photoelectric conversion element, such as a CCD sensor, provided in the digital color copying machine. Moreover, providing a film projector on a conventional analog copying machine and copying the film images as projected by the film projector has been known in the art, as well as printing the images by applying the projected images directly to a photosensitive material.
Further, it is noted that films, in general, have a more extensive density range than that of an original sheet copied by reflection. Moreover, this factor, i.e. the density range, is different from one type of film to another, such as negative film and reversal film. For instance, the density range on reversal film is wider than that of negative film. Moreover, the relation between the amount of exposure to light (H) for the photographed object, which corresponds to the density of the photographed object, and the density D of the film shows a linear characteristic in the region with luminosity, but assumes a nonlinear characteristic in the other region. In other words, the photographing characteristic of a film (the H-D characteristic) is not necessarily linear in any region of luminosity.
Furthermore, when nonprofessionals take photographs with a camera, they tend to set the camera for the wrong amount of exposure, i.e. either with an excessive amount of exposure or with an insufficient amount of exposure. Above all, when a negative film is exposed with an insufficient amount of light, a copy produced by optically reading the film having a picture taken of a person's face will present a flat copy image with no clear definition of the image with the hair rendered in paler color since the H-D characteristic of the film is nonlinear in this region of luminosity, as mentioned above.
On the other hand, when light is projected from the film projector, with the film put in close contact on the prescribed position on the platen, in an attempt at producing a copy of an image on negative film in the contact print mode, the area of the platen which the film does not cover will eventually be subjected to back-lighting. In consequence of this, the copying of this film in this state will render the back-lighted area in black, since the negative-positive reversal process is applied to this area, with the result that the copy s produced will be unsightly and also toner will be wasted.
Moreover, when it is attempted to produce a copy by projecting light from a film projector upon a reversal film placed in close contact, for example, on the platen of a copying machine, the area not covered with the film will be back-lighted and the light from the lamp will directly pass through. Because of this, there develops a difference in density between the area covered with the film and the area where the film is not present, with the result that the area not covered with the film will be rendered brighter than the area where the film is present. Although it is conceivable to perform the detection of the position of the film by reading this difference in density, it requires troublesome operations because this process calls for operations in two different modes, one in the reflected original sheet mode (in which the image is darker than the original sheet) in which the background is processed as black, and the other in the film mode (in which the background is brighter than the original sheet).